Field of the Invention
The present invention relates to wireless communications, and more specifically, to a method and apparatus for transmitting uplink control signals in a wireless communication system.
Related Art
Universal mobile telecommunications system (UMTS) is a 3rd generation (3G) asynchronous mobile communication system operating in wideband code division multiple access (WCDMA) based on European systems, global system for mobile communications (GSM) and general packet radio services (GPRS). A long-term evolution (LTE) of UMTS is under discussion by the 3rd generation partnership project (3GPP) that standardized UMTS.
The 3GPP LTE is a technology for enabling high-speed packet communications. Many schemes have been proposed for the LTE objective including those that aim to reduce user and provider costs, improve service quality, and expand and improve coverage and system capacity. The 3GPP LTE requires reduced cost per bit, increased service availability, flexible use of a frequency band, a simple structure, an open interface, and adequate power consumption of a terminal as an upper-level requirement.
Small cells using low power nodes are considered promising to cope with mobile traffic explosion, especially for hotspot deployments in indoor and outdoor scenarios. A low-power node generally means a node whose transmission (Tx) power is lower than macro node and base station (BS) classes, for example a pico and femto eNodeB (eNB) are both applicable. Small cell enhancements for the 3GPP LTE will focus on additional functionalities for enhanced performance in hotspot areas for indoor and outdoor using low power nodes.
In light of operator's big interest in deploying small cells overlaid in a macro cell, some issues are identified for small cell enhancements. One of the issues is to introduce user equipments (UEs) having dual connectivity to a macro cell and small cells. For example, the UE has one connectivity to a macro cell for control plane aspects and another connectivity to a small cell for user plane aspects.
If such dual connectivity is supported, different cells may play different roles. Therefore, functional spit for cells needs to be defined.